Field of the Invention
The present invention relates to methods of collecting photometric image data and determining light exposure. More specifically, the present invention relates to a method of collecting photometric image data which is used when a color original image is divided into a large amount of picture elements, or pixels, for photometry of the color original image in order to copy the color original image on color copy material or black-and-white material, and relates to a method of determining the light exposure by extracting feature image data such as density data of a person's face when copying the color original image on the color copy material or the black-and-white copy material.
Background Information
It is necessary to expose a color original image with appropriate light exposure in order to copy the color original image on copy material. In conventional methods, the color original image is divided into hundreds of picture elements so that the light exposure desired for copying the color original image can be determined depending upon photometric data which is obtained by photometry per the color original image.
In viewing a portrait, primary attention is paid to the person's face. Therefore, it is necessary to print of the person's face in appropriate color and density in order to provide a which is superior in quality.
For printing the person's face in appropriate color and density, there has been proposed a method of extracting the person's face by extracting flesh-colored data (see Japanese Patent Application Laid-Open Nos. 52-156624, 52-156625, 53-12330, 53-145620, 53-145621 and 53-145622). In these publications, the color original image is divided into many photometric points and the respective photometric points are divided into three colors, i.e., R (red), G (green) and B (blue) for photometry of the photometric points. It is decided by calculating depending upon the photometric data whether each color of the photometric points is within the range of flesh-color. Subsequently, a cluster of the photometric points which are decided to be in the range of flesh-color are defined as density data of the face.
Another method is also disclosed in Japanese Patent Application Laid Open No. 2-287531 (U.S. patent application Ser. No. 07/515,897, U.S. Pat. No. 5,128,711). In this publication, the cluster of the photometric points which are decided to be in the range of flesh-color is compared with a face size. The face size is estimated on a photographic original image depending upon focal length data and subject distance data. Based on the comparison, it is decided whether or not the cluster of the photometric points is the face region.
However, since the color within the range of flesh-color is defined as the density data of the face in the conventional method, portions except the face having the flesh-color or color similar to the flesh-color, i.e., ground, a branch of a tree, clothes or the like may be also extracted as density data of the face. As a result, data may be extracted inaccurately.
In addition to the method set forth above, a method is known in which it is decided that the color original image is the face if the respective pixels having the same density information form a circle. In the method, a region of the face may be extracted inaccurately because a shape of the exposed flesh-color portion of the face is varied depending upon a condition in photographing, and the shape of the exposed flesh-color portion may not be circular, i.e., the face may be partially obscured.
Further, if the face has a small size, it is necessary to divide the color original image into several tens of thousands of picture elements for photometry when determining light exposure by extracting the person's face.
However, when the color original image is finely divided for the photometry, the photometry with the same size of the picture element is naturally provided for positions irrelevant to a main image such as face in the color original image. If the face has a small size, photometric data unnecessary for determination of the light exposure is increased. Accordingly, disadvantages may occur in analysis of the color original image and the face may be erroneously extracted. On the other hand, if the face has a large size, as the same photometric data obtained from the face position increase, fine photometry would be naturally provided for the positions unnecessary for determination of the light exposure, i.e., the positions except the face. As a result, efficiency of determining the light exposure is reduced.